Learning Objectives

Have you ever cut yourself accidentally?


What came out of the wound? The fluid that came out of your wound is blood.






Blood is red and quite viscous (thick). Blood is called the fluid of life. If you had no blood, you would not be alive. Blood reaches the different parts of your body, through your circulatory system.

In this system page you will study the parts of the circulatory system. You will also learn more about the functions of the circulatory system. You will also discover some injuries and diseases that can affect the circulatory system and ways by which to take care of this system.



Without your being aware of it, your organ systems are working continuously to keep you alive. One of these organ systems is the circulatory system.

The heart never stops beating as long as a person is alive. It starts beating when a child is still inside its mother’s womb. When you are excited your heart beats faster. The heart pumps approximately 70 times a minute. In this period, it is able to pump around 5 liters of blood. That is about 100,800 times each day! When you are exercising rigorously and your body cells need a higher rate of blood flow to obtain more oxygen, nutrients and food, the heart pumps more rapidly to force more blood around your body faster.The heart will pump up to 200 times per minute to move 40 liters of blood around your body if it has to. The heart is the most important part of the circulatory system.


Do you know what your heart looks like? Clench your fist and look at it. That’s approximately the same size as your heart.

Your heart is a pear-shaped organ that lies between your lungs. It is slightly tilted to the left. The heart is actually made up of two pumps that work together. These two pumps are separated by a muscular wall called septum. The right pump collects blood from the body and sends it to the lungs. The left pump collects blood from the lungs and sends it to the rest of the body.

Each pump has two chambers: the atrium and the ventricle. The atrium has a thin wall while the ventricle has a thick one. Each atrium receives and stores blood. Each ventricle, on the other hand, pumps blood away from the heart. The atria and the ventricles are separated by one-way valves.

Do you know how a heartbeat sounds? It usually sounds like lub-dub. This sound is produced by the closing and opening of the valves in the heart.

Roles

Roles of the Circulatory System:The circulatory system is divided into two systems

• The pulmonary: includes the right atrium and ventricle, pulmonary trunk, two pulmonary arteries, and four pulmonary veins. The blood is pumped to the lungs where the gas exchange is made, and oxygenated blood is returned to the heart.
• The Systemic: includes the left atrium and ventricle, the aorta, and all the arteries and veins that supply the body until it reaches the heart again.

Arteries: carry oxygenated blood away from the heart.They are also more elastic than veins
Veins: carry poorly oxygenated blood back to the heart

Do you know that if you were to take out all your blood vessels and line them up end to end,
they would be able to go around the earth twice?


**Tip on remembering the direction of blood flow through the heart "When it leaves the right, it comes right back, but when it leaves the left, it is left."

THERE ARE THREE TYPES OF BLOOD VESSELS IN THE BODY: the arteries, veins and capillaries.

Arteries are what we call efferent vessels because they carry blood away from the heart. Every time your heart beats, blood is pumped into your arteries. The walls of the arteries stretch as the blood comes in. As it passes by, the walls relax. The stretching and relaxation of the artery wall is the pulse. You feel your pulse at your temples, neck and wrists.

The veins are called afferent vessels because they bring back blood toward the heart. Most veins carry poorly-oxygenated blood except for the pulmonary vein which carries oxygen-rich blood from the lungs to the heart. Large arteries branch into smaller arteries called arterioles; large veins branch into smaller veins called venules. These arterioles and venules lead into capillaries,the smallest of all blood vessels.

Capillaries, are located mostly between the veins and the arteries. Their job is to distribute oxygen rich blood that comes from the arteries out into the tissues of the body.Then, they move the oxygen-depleted blood from the tissues back into the veins.

Video and Slides

Circulatory Pathology

http://www.smm.org/heart/heart/pumping-f.htm

Case Study

Case study #13
Case study #14
Case study #21

In the News

Air pollution may cause blood clots in legs

Sleep apnea linked to heart risks in children

Glossary

Internal elastic lamina: Separates the tunica intima from the tunica media.

External elastic lamina: Separates the tunica media from the tunica externa.

Systematic circulation: Consists of the blood vessels that extended from the body.

Pulmonary circulation: Consists of the vessels that take the blood to and from the lungs for the purpose of gas exchange.

Anastomosis: Is the side where two or more arteries (or two or more veins) merge to supply the same body region.

Arterial anastomoses: Provide alternate blood supply routes to the body tissues or organs.

End arteries: Are arteries that do not form anastomoses, there is only one pathway through which blood can reach an organ.

Functional end arteries: These arteries (such as the coronary arteries in the heart wall), have anastomoses that are so tiny that the arteries may almost be considered end arteries.

Companion vessels: An artery that will travel with a corresponding vein because they supply the same body and tend to lie next to one another.

Lumen: (loo'men) The tunics surround the lumen,or inside the space,of the vessel through which blood flows.

Tunica intima: (too'ni-ka in-ti'ma;intimus=inmost),or tunica interna. It is the innermost layer of a blood vessel wall. It is composed of an endothelium (a simple squamous epithelium lining the blood vessel lumen) and a subendothelial layer made up of a thin layer of areolar connective tissue.

Tunica media: (me'de-a;medius=middle) is the middle layer of vessel wall. It is composed of circulatory arranged layers of smooth muscle cells.

Tunica externa: (eks-ter'na;externe=outside),or tunica adventitia. It is the outer most layer of the blood vessel wall. It is composed of an areolar connective tissue that contains elastic and collagen fibers.

Arteries: The arteries in the systemic circulation carry oxygenated blood to the body tissues. However, the pulmonary arteries (part of the pulmonary circulation) carry deoxygenated blood to the lungs. Arteries have three basic types ans are elastic arteries, muscular arteries, and arterioles.

Elastic arteries: These are the largest arteries, with diameters ranging from 2.5 to 1 centimeter. They are also called conducting arteries because they conduct blood from the heart to the smaller muscular arteries.

Muscular arteries: They typically have diameters ranging from 1 centimeter to 3 millimeters. These medium-sized arteries also called distributing arteries because they distribute blood to the body organs and tissues.

Arterioles: They are the smallest arteries,with diameters ranging from 3 millimeters to 10 micrometers. In general, arterioles have less than six layers of smooth muscle in their tunica media.

Capillaries: Are the smallest blood vessels, connect arterioles to venules. The average capillary diameter is 8-10 micrometers, just slightly larger than the diameter of a single erythrocyte. Most capillaries consist solely of a tunica composed of a very thin, singer layer of epithelium and a basement membrane; there is no subendothelial layer. The thin wall and the narrow vessel diameter are optimal for diffusion gases and nutrients between blood in the capillaries and body tissues. They are three types of capillaries: Continuous capillaries, Fenestrated capillary, and Sinusoid.

Continuous capillaries: It is the most common type, this have tight junctions between the endothelial cells that permit minimal fluid leakage, continuous capillaries are found in muscle, skin, the thymus, the lungs, and the CNS.

capillaries: These types have "holes" in the endothelial cells to permit small molecules to move out of the vessel. Fenestrated capillaries are seen where a great deal of fluid transport between the blood and interstitial tissue occurs, such as in the small intestine (intestinal villi), the ciliary process of the eye, most of the endocrine glands, and the kidney.

Sinusoids: Or discontinuous capillaries, they have big gaps between the endothelial cells and a discontinuous basement membrane that promotes transport of larges molecules. Sinusoids are found in bone marrow, the anterior pituitary, the parathyroid glands, the suprarenal glands, the spleen, and the liver.

Veins: These drain capillaries and return the blood to the heart. Compared with a corresponding artery, vein walls are relatively thin, and the vein lumen is larger.

Systematic veins: These carry poorly oxygenated blood to the right atrium heart, while pulmonary veins carry oxygenated blood to the left atrium of the heart.

Blood reservoirs: Because blood pressure gradually decreases as blood travels through smaller arteries and in to capillaries, the pressure has been substantially reduced by the time blood reaches the veins. At rest, the body's veins hold about 60% of the body's blood. Thus, veins function as blood reservoirs.

Venules: Are the smallest veins, measuring from 8 to 100 micrometers in diameter. Venules are companion vessels with arterioles since both supply the same areas and are similar size. A venule becomes a "vein" when its diameter is greater than 100 micrometers. Smallest and medium-size veins typically travel with muscular arteries, while the largest veins travel with (correspond to) elastic arteries.

Postcapillary venules: They are the smallest ones, drain capillaries. Postcapillary venules resemble continuous capillaries in structure, except that they have a slightly wider lumen.

Diapedesis: Is the mechanism in which leukocytes migrate from blood vessels in to interstitial fluid, occurs primarily in the post capillary venules.

Valves: This formed primarily of tunica intima and strengthened by elastic and collagen veins. Valves are one-way flaps that prevent pooling and backflow of venous blood to ensure that blood flows toward the heart.

Skeletal muscle pump: Particularly in the lower limbs, the contraction of skeletal muscles squeezes the veins passing between muscles and forces blood toward the heart.

Blood Flow through the Heart

Superior Vena Cava: receives blood from the head and upper body and drains it into the right atrium.

Inferior Vena Cava: receives blood from the legs and trunk and drains it into the right atrium.

Coronary Veins: return deoxygenated blood from myocardium to coronary sinus.

Coronary Sinus: receives venous blood from the veins within myocardium and drains into the right atrium. (All of the above bring blood to the heart and dump it into the Right Atrium)

Right Atrium: superior chamber of the heart that receives blood from the vena cavae and coronary sinus.

Right Atrioventricular (tricuspid) Valve: located between the right atrium and right ventricle, prevents back flow into the right atrium during ventricle contraction.

Right Ventricle: right inferior portion of the heart, sends blood to the pulmonary trunk.

Pulmonary Valve: prevents back flow of blood from the pulmonary trunk to the right ventricle during ventricular relaxation

Pulmonary Trunk: a large vessel on the anterior superior portion of the heart that receives blood from right ventricle and directs to the lungs via the pulmonary arteries.

Pulmonary Arteries: paired branches of the pulmonary trunk that direct deoxygenated blood to the lungs to be oxygenated. (One of the few places that deoxygenated blood gets carried by arteries.)

Pulmonary Veins: two vessels from each lung that return oxygenated blood to the heart's left atrium. (One of the few places that oxygenated blood gets carried by veins.) Left Atrium: receives blood from the lungs via the pulmonary veins.

Left Atrioventricular (bicuspid or mitral) Valve: located between atrium and ventricle on the left side, prevents back flow of blood into the left atrium during ventricular contraction.

Left Ventricle: Composed of an unusually thick myocardial wall for contraction against high pressure.

Aortic Valve: three half-moon shaped cusps that prevent back flow of blood from the aorta to the relaxed left ventricle.

Ascending Aorta: receives blood immediately from the ascending aorta. supply blood to the myocardium.

Aortic Arch: curved portion of the aorta that extends superior and posterior to the pulmonary trunk.

Descending Aorta: portion of the aorta that descends from the aortic arch and continues inferiorly until it divides into the common iliac arteries.

Major blood vessels involved in blood flow to and from all the body tissues

General Arterial Flow Out of the Heart:

• The ascending aorta gives off the left and right coronary arteries to supply the heart.

• The aortic arch has three branches: the brachiocephalic trunk, the left common carotid artery,and the left subclavian artery.

• The descending thoracic aorta extends several branches to supply the thoracic wall. Inferior to the diaphragm, it is renamed the descending abdominal aorta.

• Bifurcation of the descending abdominal aorta yields paired common iliac arteries.

General Venus Return to the Heart:

• Deoxygenated blood returns to the heart via the superior and inferior venae cavae.

Blood flow through to the Head and Neck:

• Common carotid arteries branch into the internal and external carotid arteries, which supply most of the blood to the head and neck via other smaller arteries.

• Cerebral arterial circle (circle of Willis) is an arterial anastomosis that supplies the brain.

• Vertebral veins and the dural venous sinuses drain the internal jugular brain.

• External and internal jugular veins merge with the subclavian vein to form the brachiocephalic vein.

Blood Flow Trough the Thoracic and Abdominal Walls:

• Thoracic and abdominal walls are supplied by paired arteries. An unpaired median sacral artery supplies the sacrum and coccyx.

• Hemiazygos and accesory hemiazygos veins drain the left side of the thorax and the azygos vein drains the right side of the thorax.

Blood Flow Through the Thoracic Organs:

• Bronchial arteries and bronchial veins supply lung connective tissue.

• Esophageal arteries and veins supply the esophagus.

• Superior phrenic arteries, the musculophrenic arteries, the pericardiacophrenic arteries, and the inferior phrenic arteries and veins of the same supply the diaphragm.

Blood Flow Through the Gastrointestinal Tract:

• Three unpaired arteries have branches that supply the gastrointestinal tract organs: these arteries are the celiac trunk, the superior mesenteric artery.

• The hepatic portal vein is a large vein that receives this oxygen-poor but nutrient-rich blood from the gastrointestinal organs. Three main vein merge to form the hepatic portal vein: the inferior mesemteric vein, the splenic vein, and the superior mesenteric vein. Blood exits the liver via hepatic veins.

Blood Flow Through the Posterior Abdominal Organs, Pelvis, and Perineum:

• Paired branches of the descending abdominal aorta supply the posterior abdominal organs and the pelvis and perineum. Venous drainage is by veins of the same name as the arteries.

Blood Flow Through the Upper Limb:

• The subclavian artery continues as the axillary artery after it passes the lateral border of the first rib; it becomes the braquial artery when it passes the inferior border of the teres major muscle. In the cubital fossa, this artery divides into an ulnar artery and radial artery.

• An anastomosis of ulnar and radial arteries forms the superficial palmar arch and the deep palmar arch; digital arteries emerge from the arches to supply the fingers.

• The superficial group of veins contains the basilic, median cubital, and cephalic veins that drain into the axillary vein. The deep group of veins contains veins that bear the same as the arteries.

Blood Flow Through the Lower Limb:

• The external iliac artery extends inferior to the inguinal ligament and is renamed the femoral artery. It enters the popliteal fossa, and then becomes the popliteal artery before dividing into anterior and posterior tibial arteries. The posterior tibial artery gives off a fibular artery and continues inferiorly, where it branches into medial and lateral plantar arteries.

• The superficial group of veins includes the great saphenous vein and the small saphenous vein. The deep group of veins consists of veins that bear the same names as the correspondingarteries.

Pulmonary circulation vessels and their pathways

1. The pulmonary circulation is responsible for carrying deoxygenated blood from the right side of the heart to the lungs.
2. The newly oxygenated blood is then returned to the left side of the heart.
3. The pulmonary arteries divide into smaller arteries that continue to subdivide to form arterioles.
4. The capillaries merge to form venules and then the pulmonary veins.
5. Compared to the systemic circulation, the vessels that make up the pulmonary circulation are relatively short.
6. The reason for the vessels being short is because blood doesn't need to be pumped as far in the pulmonary circulation since the lungs are close to the heart.
7. The pulmonary arteries have less elastic tissue and wider lumens than the systemic arteries.
8. Blood pressure is lower in the pulmonary arteries than in the systemic arteries so the pressure is lower on the right side of the heart compared to the left side.

1.
1. What fruit shape is your heart more like?
a. banana
b. a apple
*c. a pear
d. a orange

2. What is the circulatory system?
a. The body`s system of nerves
b. The body`s food-processing system
*c. The body`s blood-transporting system
d. The body`s breathing system

3. Which type of blood vessels carries blood from the heart?
a. Capillaries
*b. Arteries
c. Veins
d. All of they above

4. Why is the blood flowing from the lungs to the heart bright red rather than dark?
a. Carbon dioxide makes it red.
b. Oxygen makes it red.
c. The lungs add a pigment to blood as it flows through them.
d. Gastric juices produce the red color of blood.

5. Which of the following can best be compared to soldiers?
a. Capillaries
b. Red blood cells
*c. White blood cells
d. Lungs

6. What is the main job of the red corpuscles in the blood?
a. To fight disease
b. To clot blood
c. To transport carbon dioxide to the body`s cells and carry away oxygen from the cells.
d. To transport oxygen to the body`s cells and carry away carbon dioxide from the cells.

7. The heart is divided into how many chambers?
*a. Four - two atrium and two ventricles
b. Five - three atrium and two ventricles
c. Two - one atrium and one ventricle
d. Three - one atrium and two ventricles

8. What are capillaries?
a. The medical name for heart muscle cells.
*b. The smallest blood vessels of the circulatory system.
c. Small lumps of fatty tissue that can clot blood vessels.
d. They help to clot the blood

9. Which blood vessels contain one-way valves to stop the blood from travelling backwards?
a. Capillaries
b. Veins
c. Arteries
*d. Ventricles

10. What is blood pressure?
a. The ratio of oxygen to carbon dioxide within the blood.
b. The concentration of red blood cells within the blood.
*c. The amount of pressure exerted on blood vessel walls as the blood is pumped around.
d. The concentration of white blood cells within the blood.

11. Which type of capillaries have holes within each endothelial cell?
a. Continuous capillaries
*b fenestrated capillaries
c. sinusoid capillaries
d. all at above

12. How many different classes of blood vessels are there?
a. 2
b. 5
c. 3
*d. 4

13. Which site is where two or more arteries (or two or more veins) merge to supply the same body region?
a. end arteries
*b. anastomosis
c. functional end arteries
d. companion vessels

14. Which type of vessel has a large number of smooth muscle cell layers in its tunica media as well as elastic tissue confined to an internal elastic lamina and external elastic lamina?
a. elastic artery
*b. muscular artery
c. arteriole
d. venule

15. Which of the following is not true about blood vessel tunics?
a. They are a network of small arteries, called the vasa vasorum.
b. They are found in arteries and veins.
c. They have an innermost layer, and outermost layer, and a middle layer.
*d. They are all correct.